1. Field of the Invention
The present invention relates to a variable optical attenuator for use in optical fiber communication and optical network, and particularly to a variable optical attenuator with stabilizing mechanism.
2. Description of Related Art
An optic attenuator is a passive optical component for reducing optical power propagating in a fiber, and may perform fixed or variable attenuation of optical signal. Optical attenuators are widely used in optical transmission and optical networks.
A general variable optical attenuator comprises a filter. The filter has an effective filter region located in an optical path between a collimator and a reflector. The filter has a filter density which increases from a low density region to a high density region. An optical signal can be attenuated to different extents by transmitting through different region of the filter.
U.S. Pat. No. 6,130,984 discloses a variable optical attenuator. A variable neutral density filter element is mounted on a wiper actuation mechanism so that it moves along a linear axis perpendicular to an input fiber and an output fiber. A geared electric motor drives the wiper actuation mechanism to move the filter. As the filter moves, optical signals from the input fiber to the output fiber intersect the filter at different places varying between a low density region and a high density region, thereby attenuating the optical signals to different extents. A disadvantage of the attenuator is that no means is devised to stabilize the wiper actuation mechanism. Thus as the wiper actuation mechanism moves the filter, the filter can be rotated out of plane. This in turn results in an attenuation of the optical signals which is different from that expected.
The present invention provides a stabilizing mechanism which prevents the filter from rotating out of plane, thereby ensuring the attenuation precision.
An object of the present invention is to provide a variable optical attenuator having a stabilizing mechanism for preventing the filter from undesired rotation.
A variable optical attenuator of the present invention comprises a cover, a housing, an optical module, a reciprocating means, a filter and a fixer.
The housing defines an interior space forming an inner cavity in a lower portion of the housing. A pair of locating slots is defined in opposite lateral sides of the inner cavity. An inner sidewall forms a forward boundary of the inner cavity. A side hole communicates between one of the locating slots and an outside wall of the housing. A fixing groove and a supporting portion are formed adjacent the other locating slot.
The optical module comprises a frame, a reflector and a collimator. The frame has a groove with an inner wall, and a through hole communicating with the groove. The reflector is fixed on the inner wall of the frame and is disposed coaxially with the through hole. The collimator is positioned in the through hole and fixes ends of an input optical fiber for carrying the transmission optical signals to the attenuator and an output optical fiber for receiving the resulting attenuated transmission optical signals from the attenuator.
The reciprocating means comprises a carrier for carrying the filter, a stopper mechanism, a stabilizing mechanism, and a screw rod. The stopper mechanism has two stopper blocks and a stopper body. The stabilizing mechanism has a fixing portion for being fixed to the carrier and a mating portion for contacting the housing. The screw rod has a screw portion at its middle and a holding portion at each end.
When assembled, the carrier moves lengthwise along the screw rod when the screw rod is rotated. The filter is fixed onto the carrier and moves along with the carrier. The stopper mechanism is formed around three sidewalls of the carrier. The stabilizing mechanism is mounted on the carrier. The fixing portion of the stabilizing mechanism is inserted into a fixing groove of the carrier. The mating portion of the stabilizing mechanism abuts against the inner sidewall and moves along the inner sidewall when the carrier is moved.
By rotating the screw rod first in one direction and then in the reverse direction, the carrier with the filter and the stabilizing mechanism can be made to move first toward one side and then toward another side of the housing. The direction of movement of the filter is perpendicular to the path of the input and output light. The filter has a filter density which varies between a low density region and a high density region along a linear filter axis. When the carrier arrives at one end of the screw rod, the stoppers abut with surfaces of the corresponding locating slot and the part of the filter penetrated by the input and output light will be either the low density region or the high density region. During rotation of the screw rod, the stabilizing mechanism prevents the carrier from rotating with the screw rod and provides for stable movement of the filter, thereby assuring precision adjustment of attenuation of optical signals.
Other objects, advantages and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings, wherein.